“[Writing is] an art, not an inspiration. It is a trade, so to speak, & must be learned — one cannot ‘pick it up.’ Neither can one learn it in a year, nor in five years. And its capital is experience. . . . Whatever you have lived, you can write — & by hard work & a genuine apprenticeship, you can learn to write well; but what you have not lived you cannot write, you can only pretend to write it.”

Mark Twain, letter to Mrs. Whiteside, as quoted in letter to Olivia Clemens (10 Jan. 1885), in The Love Letters of Mark Twain 228 (Dixon Wecter ed., 1949) (via Bryan Garner, author of Garner’s Modern American Usage, in his blog)